In aqueous dispersing materials that contain functional material, the functional materials have been conventionally well known in the art, which include: agricultural chemicals such as herbicides and insecticides; pharmaceuticals such as anticancer agents, antiallergy agents, and antiphlogistic agents; and coloring materials such as ink and toner that contain colorants. In recent years, digital printing technologies have very rapidly progressed and the representative examples of the digital printing technologies include the so-called electrophotographic and inkjet technologies. The technologies, such as image-forming technologies for the office, home, and other uses have further increased their raison d'etre.
Among the technologies, the ink-jet technology as a direct recording method has prominent characteristic features of compactness and low power consumption. In addition, the image quality has rapidly increased with the advances in the micro-fabrication of nozzles. One example of the ink-jet technologies is a method in which ink supplied from an ink tank is vaporized and bubbled by heating with a heater in a nozzle to discharge ink to form an image on a recording medium. Another example is a method in which ink is discharged from a nozzle by vibrating a piezo-electric element.
The ink used in those methods is typically an aqueous dye solution, so that the ink may run on a recording medium when colors are superimposed thereon or a phenomenon referred to as feathering may occur on a recording area of the recording medium in the direction of paper fibers. For alleviating this problem, U.S. Pat. No. 5,085,698 discloses the use of pigment-dispersion ink. However, many improvements are still desired.